The invention relates to a motor vehicle wheel disc with arms, in particular for passenger car, formed in one piece from embossed sheet metal, which represents an excellent compromise in terms of weight, cost, style or freedom of possible added styling (decorative wheel cover for example).
In the designing of a sheet metal wheel for a motor vehicle, the general aim is to optimise the weight and cost of such a product. The development of embossing techniques, numeric simulation means, and materials has led to great progress over the last few years. However, the majority of products has remained within the concept of a substantially axisymmetric disc (i.e. one whose cross-sectional profile is virtually fixed in form), comprising perforations and sometimes embossing in the upper part.
This type of profile does not give the product a very enhanced style or image, which explains in most cases why manufacturers resort to a decorative wheel cover placed on the product when it is mounted on the vehicle.
One can count several attempts to create style directly from the sheet metal forming the wheel disc by forming deep embossed areas forming stiffeners and/or a particular assembly of the disc with the rim (under-seat, “full-face” assembly (i.e. disc whose radially outer edge includes the outer flange and seat of the rim), with the rim welded at the end, etc.) and sometimes associated with effects connected to painting. These attempts have not yet led to generalisation for reasons of excessive weight or difficulties in execution.
In general, the market for styled wheels for passenger cars is confined to the use of aluminium alloys. The process of manufacture (moulding, forging etc.) of these discs allows very broad freedom of style at reasonable weights, but has the disadvantage of being 4 to 8 (even 10) times more expensive.
The specification of DE 201 08 995-U discloses a wheel whose disc is formed from a single piece of embossed sheet metal, with an outer face and an inner face. This disc has a radially outer circular assembling part intended to be connected to a rim, a radially inner part for fixing and centering to a wheel hub with a bearing area having a given number of fixing apertures and ending radially inwardly with an edge which is turned axially outwardly or centering vent (aperture), and spokes connecting the inner and outer parts, each arm being disposed substantially opposite to one of the fixing apertures and the radially inner free edges of the radially outer circular part defining perforations with the free lateral edges of the arms. This disc has a substantially circular, plane bearing region and each arm comprises two lateral stiffening elements which extend radially from the bearing area to the radially outer circular assembly part and are disposed on either side of an intermediate strip axially set back towards the interior of the disc.
Although freedom of styling either bare or with an attached part (decorative wheel cover for example) is apparently obtained, such a disc has the disadvantage of requiring a relatively thick sheet metal to be able to withstand the forces to which it is subjected during operation, in particular in the joining region between the arms and the radially inner part for fixing and centering the disc.
Hereinafter:                the “outer face” of the disc will refer to the surface of revolution generated by rotation about the axis of rotation of the disc of the regions of the disc disposed axially outermost;        the “internal face” of the disc, to the side of the disc oriented inwards, in particular the internal face of the bearing region is intended to come into contact with the outer surface of the wheel hub to which the disc is to be fixed;        and the “external face” of the disc, to the side of the disc oriented outwards, which side is visible when the wheel is mounted on the vehicle.        